Best of Both (BOB) Trial: A Feasibility Study of Hybrid High Dose Rate Brachytherapy and Stereotactic Ablative Body Radiotherapy for Low- and Intermediate-Risk Prostate Cancer

This is a single arm study. All participants will receive 1 administration of high dose rate (HDR) brachytherapy and 1 fraction of stereotactic ablative body radiotherapy (SABR). HDR brachytherapy is a form of radiation treatment. Under general or spinal anaesthesia, patients will have a urinary catheter inserted, and placement of a rectal spacer between the prostate and rectum to reduce radiation exposure to the rectum. Then 18-22 thin hollow needles will be inserted into the prostate through the perineum, through which a radiation source will be passed to deliver radiation directly to the prostate. After radiation, all needles will be removed, and three small gold markers, about the size of a grain of rice, will be implanted into the prostate. These will act as a permanent high contrast reference point during the SABR treatment. HDR dose will be 13.5 Gy delivered in a single fraction (treatment session). The procedure typically takes 2-4 hours. Participants will remain in hospital overnight for observation. Once bleeding has settled (usually the day after HDR brachytherapy), participants will have a CT scan and MRI so that the SABR treatment can be planned. The catheter will be removed after this, and once confirmed that the participant can empty their bladder adequately, they will be discharged from the hospital. SABR will be delivered approximately 3-4 weeks after the HDR brachytherapy. Participants will be treated as an outpatient. They will be positioned on the treatment couch in the same position as the CT and MRI performed after their HDR brachytherapy, using the gold markers for image guidance. They will receive a single fraction of external beam radiation treatment delivered by a linear accelerator. The dose received will be 13.5 Gy. This treatment is expected to take 20-30 minutes, however patients may be at the treatment centre for up to 2 hours to allow for preparation, positioning and treatment verification. After treatment participants can then return home. Treatment will be prescribed and overseen by a qualified Radiation Oncologist. Adherence to treatment will be monitored through participants' medical records. After treatment is complete, participants will commence follow up. This may be completed in clinic, or remotely via technology such as telephone or telehealth. The first follow up appointment will be the 'safety follow up', occurring 5-6 weeks after SABR. For the first year, participants will then be followed up every 3 months. In the second year, participants will be seen every 6 months, and this will complete trial involvement.